Women bear the greatest burden of new HIV infections throughout the world. Nevertheless, our understanding of the biology underlying HIV transmission and pathogenesis in women is incomplete. The overarching goal of this PO1 proposal is to unite a dynamic research team with complementary expertise that bridges HIV molecular biology, reproductive biology, immunology, and clinical and epidemiological research to address important, unanswered questions. 1) What sites in the female reproductive tract are most involved in HIV transmission? 2) What HIV properties and host factors critically affect transmission rates? 3) How do endogenous or exogenous sex hormones impact transmission frequency and do these factors modulate innate and adaptive immune responses in the female reproductive tract that counter infection? 4) Why have all tested vaginal microbicides not only failed to stop but often caused paradoxical increases in HIV infection? 5) Can the safety of new microbicide candidates be better assessed before large scale clinical testing? We hypothesize that 1) the upper female reproductive tract represents a highly permissive but understudied portal for HIV infection, 2) specific viral (Env) and host (semen peptides) factors importantly influence the success of male-to-female HIV transmission, 3) changes in sex hormone levels (progestin-only contraception) enhance HIV transmission and menopause adversely modulates both mucosal and systemic innate and adaptive immune responses to HIV, and 4) ineffective and unsafe microbicides activate common patterns of gene expression in the upper female reproductive tract, creating a cellular milieu that favors HIV transmission. Identification of these genes will permit construction of a predictive genetic signature for "microbicide harm." These hypotheses will be tested in three specific aims involving extensive cross-project collaborations. Specific Aim 1: To study viral and host factors regulating male-to-female transmission of HIV in the female upper genital tract (Warner Greene, MD, PhD);Specific Aim 2: To explore the upper female reproductive tract as a portal of HIV transmission and to assess effects of sex steroids and microbicides on these tissues (Linda Giudice, MD, PhD, and Karen Smith-McCune, MD, PhD, and Specific Aim 3: To investigate immunopathogenesis of HIV in the female reproductive tract (Barbara Shacklett, PhD). These studies will be enabled by two essential cores, the Clinical and Data Core (Ruth Greenblatt, MD) and the Administrative Core (Drs. Greene and Greenblatt). RELEVANCE: Together, these studies promise to greatly extend our understanding of the molecular, cellular, and immunological basis for HIV transmission and pathogenesis in women. This work could also propel future efforts aimed at developing effective biomedical approaches to interdict male-to-female transmission of HIV. PROJECT 1: Viral and Host Factors Promoting Male-to-Female Transmission of HIV (Project Leader: GREENE, W) PROJECT 1 DESCRIPTION (provided by applicant): Male-to-female (M->F) transmission of HIV is a major force driving expansion of the global AIDS epidemic. Our overall objective is to assess the potentially important role played by select viral and host factors in HIV transmission biology. In Specific Aim 1, HIV transmission pairs will be used to test the hypothesis that the envelope proteins from viruses successfully transmitted to women differ from non-transmitted viruses by their fusogenic properties and/or target cell selectivity. Envelopes from transmitted viruses share common features including compact V1-V4 regions, decreased numbers of glycosylation sites, and a greater sensitivity to neutralizing antibodies. These viral envelopes may be imbued with special properties that favor virion fusion to target cells within the female reproductive mucosa. In Specific Aim 2, biological features of recently identified fibrillar peptides in semen that can enhance HIV infection 10-100,000-fold will be tested. These peptides, termed semen enhancer of HIV infection (SEVI), are produced by endoproteolytic cleavage of prostatic acid phosphatase, a highly abundant semen protein. They enhance HIV infection by sharply increasing virion attachment to target cells. Our studies will test the hypothesis that SEVI propels M->F transmission of HIV and further that SEVI antagonists may impair HIV infection of women. Our studies specifically seek to: 1) identify the cellular protease(s) responsible for the generation of SEVI, 2) test whether SEVI enhances virion transcytosis, trans-infection, and cell-cell infection, 3) explore whether SEVI production varies among males and whether HIV infection alters SEVI levels, and 4) investigate novel approaches for inhibiting the action of SEVI. Effective SEVI antagonists could find application in future multicomponent microbicides designed to prevent HIV transmission to women. This project will also interact extensively with Projects 2 and 3 of this P01 application. Viruses containing primary transmitted envelopes will be provided for use in these projects. Fusion assays will be performed collaboratively to monitor effects of progestin contraceptives, menopause, and microbicides on HIV target cells within female reproductive mucosa. Semen, SEVI, and SEVI antagonists will also be profiled for potential "harm" effects on endometrial and cervical mucosa. Together, the multiple lines of investigation described in Project 1 promise to expand our understanding of the molecular basis for M->F transmission of HIV. RELEVANCE: An improved understanding of the molecular underpinnings of M??F transmission of HIV could result in new approaches for curbing HIV infection in women including rational approaches for development of female controlled microbicides and prophylactic vaccines active at mucosal surfaces.